This invention relates in general to welding and in particular to a new and useful method and apparatus for finding and following a fillet weld in a shielded arc welding process.
To control the welding torch when seeking and following a fillet weld, it is customary to employ to so-called back and forth control, whereby the welding torch tube swings across the lengthwise axis of the weld at a predetermined frequency and through a predetermined angle. In this way, the magnitude of the welding current is measured and then the vertical and horizontal position of the torch is corrected. Back and forth control has the disadvantage that it only works with high-quality gas blends as the shielding gas. If carbon dioxide is used for this purpose, instability of the arc results, which varies continually between spray arc, long arc, and short arc, as well as short circuit. Under these conditions, the current signal during the measurement of the sides of the weld can no longer be evaluated with the necessary accuracy and reliability at the end of the swinging motion, so that the torch is no longer guided with certainty down the middle of the fillet weld.